The present invention relates to a machine for knitting a seamless tubular structure of continuous fibers, but particularly high-performance fibers. Such a tubular structure may be used as a reinforcing substrate for a roofing material by impregnating it with a liquid roofing material, such as a modified bitumen. Other uses may be found for using the tubular structure as a reinforcing substrate for composite pipes, snowboards, water and snow skis, power poles, and many other reinforced structures or parts. In these other uses, the substrate will be effectively embedded into a continuous matrix of a polymeric resin system, such as an epoxy, a polyester, a phenolic material or a vinylester, for example.
It is desired to provide a tubular structure of continuous fibers, and particularly high-performance fibers, which may be flattened out to provide a two-ply knitted reinforcement substrate for a roofing material. In addition to direct drawn glass fibers or rovings, other materials which may be used would include carbon fibers, aramid-type fibers including those commercially available from duPont under the KEVLAR trademark. By xe2x80x9crovingsxe2x80x9d in the above sentence, we mean single end direct draw packages or spools of reinforcement fibers.
It is therefore an advantage of the present invention to provide a tubular knitting machine for preparing a seamless tubular structure of continuous fibers.
This and other objects of the present invention are provided by the tubular knitting machine and a tubular knitting method.
The device for knitting together a tubular structure of continuous fibers with a stitch yarn comprises a cylinder having a plurality of axially oriented holes equally spaced about a circumference of the cylinder. A plurality of needles, corresponding in number to the plurality of holes, are provided. Each needle has a latch mechanism at one end and a base at the other end. The base end of each needle is inserted into one of the holes. Each pair of adjacent needles defines an interstitial space.
The device further comprises a means for introducing a plurality of a first set of the continuous fibers to the cylinder in an effectively radial manner, with one first continuous fiber corresponding to each said interstitial space between the needles;
The device also comprises a means for introducing at least one second continuous fiber to the cylinder at an insertion point. This at least one second continuous fiber is introduced tangential to the cylinder at the insertion point.
The device also comprises a means for introducing the stitch yam to the latch mechanism of one of the needles on the cylinder adjacent the insertion point for each of the at least one second continuous fiber, as well as a cam section that interacts with the needles near the insertion point to sequentially raise and lower the base ends thereof.
The cam section and the two introducing means are rotated in a stepwise sequential manner relative to the cylinder by a means for rotating, to knit the stitch yarn around the first and second continuous fibers, forming the knitted tubular structure.
In some embodiments, the means for introducing the first continuous fibers includes a ring with a plurality of holes corresponding to the number of the plurality of first continuous fibers. The ring is concentric with the cylinder, although spaced axially away from and radially outward from the cylinder. Each hole directs one of the first continuous fibers from a feed source to one of the interstitial spaces.
In some embodiments, the device further comprises a means for drawing the knitted tubular structure axially away from the cylinder.
In some embodiments, each of the plurality of needles is a compound needle having first and second parts. In such needles, the first part comprises a base at a first end and an open notch at a second end, a channel running axially through a portion of the first part between the base and the notch. The second part comprises a cam follower at a base end thereof and a sheath member with a top end. This sheath member slidingly fits in the channel of the first part so that movement of the cam follower relative to the base causes the second part to slide within the channel, allowing the top end of the sheath member to selectively open or close the opening in the notch.
In some embodiments of the device, the stitch yarn used will be thermally fusible, in which case the device can further comprises a means for heating the knitted tubular structure as it is drawn away from the cylinder to a temperature sufficiently high to fuse the stitch yarn to itself.
The method of forming a knitted tubular structure of continuous fibers is achieved through a number of steps. In one step, a plurality of a first set of the continuous fibers are introduced effectively radial to a cylinder having a plurality plus one of latch needles disposed in incremental spacing about a circumference thereof. These first continuous fibers are introduced so that one of the first continuous fiber passes through an interstitial space defined by a pair of adjacent latch needles. Then, the method introduces at least one second continuous fiber to the cylinder effectively tangentially thereto at an insertion point. A stitch yarn is introduced to a latch mechanism of one of the latch needles on the cylinder adjacent the insertion point for each of the at least one second continuous fiber. By manipulating the latch needles and stitch yarn adjacent to the insertion point, the stitch yarn is knitted about the first and second continuous fibers to form the tubular structure.
In some embodiments, the step of manipulating the latch needles and stitch yarn is achieved by rotating the insertion point for each said at least one second continuous fibers in a stepwise sequential manner around the circumference of the cylinder.
In some embodiments, the method also includes the step of drawing the knitted tubular structure away from the cylinder.
In some embodiments in which the stitch yam is thermally fusible, the method includes the step of heating the knitted tubular structure as it is drawn away from the cylinder to a temperature sufficiently high to fuse the stitch yarn to itself.